The invention relates to a laser pulse shaper device, which is configured for shaping laser pulses, in particular to a laser pulse shaper device including a shaper unit with dispersive elements and a light modulator for spectrally resolved modulating spectral components of the laser pulses. Furthermore, the invention relates to a shaping method for shaping laser pulses, in particular using an arrangement of dispersive elements and including a spectrally resolved modulation of the laser pulses. Applications of the invention are available in optical set-ups for stretching or compressing laser pulses, in particular in pulse amplifiers.
For describing the background of the invention, particular reference is made to the following publications:
[1] R. L. Fork et al. in “Optics Letters” vol. 9, 1984, p. 150-152;
[2] R. Naganuma et al. in “Optics Letters” vol. 16, 1991, p. 738-740;
[3] U.S. Pat. No. 8,514,898 B1;
[4] US 2001/026 105 A1;
[5] US 2007/014 317 A1;
[6] T. Binhammer et al. in “IEEE Journal of Quantum Electronics” vol. 41, 2005, p. 1552-1557;
[7] T. Baltuska et al. in “Optics Letters” vol. 27, 2002, p. 306-308; and
[8] R. Riedel et al. in “Optics Express” vol. 21, 2013, p. 28987-28999.
The generation of high-power ultrashort laser pulses (laser pulses having a pulse duration below 100 fs) by optical parametric pulse amplification (OPA), in particular using optical parametric chirped pulse amplification (OPCPA) and non-collinear OPA (NOPA), is generally known. Broadband seed laser pulses typically are amplified with narrowband pump laser pulses in a dielectric crystal. As the narrowband pump laser pulses have a longer pulse duration compared with the seed laser pulses, there is a need for temporal shaping the seed laser pulses to match the temporal pump laser pulse amplification window of the dielectric crystal. Typically, a pulse stretcher is used for stretching the seed laser pulses. The stretcher comprises a pair of dispersive prisms, which are arranged for spatially dispersing the spectral components of the seed laser pulses and re-collimating the dispersed components, as described e. g. in [1] to [5]. Along the beam path in the stretcher, the different spectral components have different beam path lengths resulting in a longer pulse duration. After the amplification, the ultrashort laser pulses are re-compressed using a pulse compressor. A pulse compressor also may comprise a pair of dispersive prisms which are arranged for introducing a chromatic dispersion to the laser pulses (see e. g. [7]).
Stretching the seed laser pulses does not only require a separation of the spectral components on a timescale, but also a control of the spectral phase and amplitude of the spectral components such that the ultrashort laser pulses can be formed by the re-compression after the OPA process. Correspondingly, there is an interest in controlling the spectral components of compressed laser pulses. It is generally known to use a spatial light modulator (phase mask) for controlling the spectral phase and amplitude of the dispersed spectral components with spatial resolution.
Conventionally, the tasks of stretching the seed laser pulses and controlling the spectral phase and amplitude are solved by separate measures. While the dispersive elements are optimized for stretching the pulses, a so-called “4-f-geometry” is used for the phase and amplitude modulation (see e. g. [6]). With the 4-f-geometry, the phase mask for spectrally resolved modulating spectral phases of the pulses is arranged in a Fourier plane of a combination of the dispersive elements and additional focusing elements. The 4-f-geometry has disadvantages in terms of a long beam path and therefore low stability of the spatial and temporal pulse properties. As a further disadvantage, a large amount of additional higher-order dispersion is added to the laser pulses, which may result in problems with the re-compression thereof.
A compact pulse compressor or stretcher can be obtained by an optical set-up including the dispersive elements and a mirror, as described e. g. in [7] and [8]. The mirror is arranged in a Fourier plane of the dispersive elements for a back-reflection of the compressed or stretched pulses via the dispersive elements. With the phase mask in the spectral Fourier plane, the spectral phase and amplitude of the spectral components can be manipulated. However, the conventional compressor or stretcher provides a diffusive line arrangement of the spectral components only. Accordingly, the manipulation in the spectral Fourier plane has a limited efficiency and precision only. This disadvantage even would be kept if the Fourier plane including the diffusive line would be imaged, e. g. with a cylinder lens onto the phase mask (as proposed in [8]) as the spatial resolution could not be improved by the focusing.